Process and device for pouring of steel from an immersion outlet

ABSTRACT

The invention relates to a process and a device for controlling the flow dispersion of a molten metal, in particular steel, which is conveyed from a melt container via a first immersion outlet part which has a polygonal, oval or circular cross-section, and an intermediate member through the second immersion outlet part which has an elongate cross-section, and flows into a stationary mold to produce slabs. The process is characterized by the following steps: (a) the central volume flow is reduced in the intake region of the second outlet part; (b) at the same time the angle of expansion (δ) of the fluid jet is increased to such an extent that the return flow in the lateral region of the intermediate member and the second immersion outlet part is substantially stopped; and (c) when the melt leaves the second immersion outlet part, it flows at a velocity profile with velocity vectors which are smaller in the opening center than the regions of the small faces. The device is characterized in that the region of the central axis (I) of the immersion outlet, the intermediate member ( 31 ) and/or the intake ( 22 ) of the second immersion outlet part ( 21 ) is equipped in such a a manner that the main flow of melt (S) leaving the first immersion outlet part is throttled.

BACKGROUND OF THE INVENTION

The invention relates to a process and a device for influencing the flowpropagation of a metallic liquid, which, flows in a guided fashion intoa stationary permanent mold from a melt container via a first immersionnozzle part, which has a polygonal, oval or circular cross section, andan intermediate part through a second immersion nozzle part, which hasan elongated cross section for production slabs.

DESCRIPTION OF THE PRIOR ART

DE 37 09 188 discloses a casting tube for metallurgical vessels which issubdivided into an upper tubular longitudinal section and a lowerrectangular longitudinal section, a conical transition being providedbetween the two longitudinal sections. The rectangular cross section canin this case have a length/width ratio of 20:1 to 80:1.

Provided at the mouth of the immersion nozzle is a transverse web whichguides the liquid steel into the lateral mouth openings. In this case,the steel enters the permanent mold with a relatively high kineticenergy. Moreover, the transverse web is subjected to a high degree ofwear.

DE 43 20 723 discloses an immersion nozzle which has a tubular shapedrefractory brick shape which is connected via a conical constructionalelement to a lower rectangular shaped refractory brick dipping into themelt. Longitudinal webs are provided in the flow cross section in thelower shaped refractory brick.

In the region of the inlet of the lower rectangular shaped refractorybrick, a transverse web is provided which reflects the flow of the meltin the direction of the widening of the flow shaft. This transverse webconfigured as a baffle disadvantageously causes strong eddies in themelt.

SUMMARY OF THE INVENTION

It is the object of the invention to avoid the disadvantages of theprior art and to create a process and a device relating to an immersionnozzle for guiding metal melts of which minimizes the turbulence in theimmersion nozzle itself and in the permanent mold, and simultaneouslythe depth of penetration of the fed melt into the liquid crater locatedin the permanent mold.

The invention achieves this object by a process which includes the stepsof reducing a central volumetric flow in a second immersion nozzle partof a metallic liquid received from a first immersion nozzle part;increasing an angle of expansion of the liquid jet so that there is noreturn flow in a lateral region of the second immersion nozzle part andan intermediate part between the first and second immersion nozzle part,and so that a velocity profile of the metallic liquid at the ouput mouthof the second immersion nozzle part is such that velocity vectors aresmaller in the center opening of the mouth than in the regions of thenarrow sides. The object is also achieved by an immersion nozzle forperforming the process.

According to the invention, in the central case of an immersion nozzlewhose mouth part dipping into the melt located in the permanent mold hasan elongated cross section, the central volumetric flow is reduced inthe inlet region of this immersion nozzle part. This reduction in thevolumetric flow is caused by throttling the central, which increase theangle of expansion of the liquid jet, specifically to such an extentthat there is essentially no return flow into the lateral region of theimmersion nozzle part having a longitudinal cross section.

As a consequence of the throttling and simultaneous spreading of thecentral volumetric flow, the melt flows from this immersion nozzle partwith a velocity profile whose velocity vectors are smaller in theopening mouth than in the regions of the narrow sides.

The quantity fed through the immersion nozzle strikes with this setvelocity profile against the liquid crater, which is located in thepermanent mold and is withdrawn in accordance with the strand withdrawalrate of 1 to 10 m/min, and penetrates at only slight depths into thisliquid crater, in accordance with a mixing length of L=0.2 to 4 m.

Owing to the intensive spreading or expansion of the central volumetricflow, the velocity profile in the region of the narrow sides has at themouth of the immersion nozzle part having an elongated cross sectionvelocity vectors which have components which permit a return flow on thenarrow sides of the permanent mold. As a result, an adequate quantity offresh melt is fed to the bath level in the permanent mold, with apositive influence on the casting powder applied to the surface.Moreover, this melt flows to the center between the immersion nozzle andpermanent mold with only a slight bow wave but in an adequate quantity.The flows of melt combine in the middle of the permanent mold and thenflow into the liquid crater in the strand withdrawal direction. There,they fill up the volumetric flow, emerging from the second immersionnozzle part, in the mouth center.

The result of this is a virtually flat and overall only shallow depthpenetration into the liquid crater, with the advantage that, forexample, in the case of a change in quality of the melt only a shortmixing length, and thus a short piece of undesired slab quality isproduced.

The throttling of the central volumetric flow is achieved by virtue ofthe fact that the region upstream of the inlet into the immersion nozzlepart having a longitudinal cross section, or the inlet itself isconfigured in a special way. In any case, the free space is keptadequately open, with the result that a defined quantity always flows inthe central region of the second immersion nozzle part.

To throttle the central volumetric flow, the wall of the broad side ofthe intermediate part arranged in the casting direction upstream of theimmersion nozzle part with an elongated cross section has a concavebulge. In an advantageous refinement, this bulge is configured in theshape of a quarter hollow sphere. In a further refinement, it has theshape of a tube segment with a prescribable contour.

The throttling is also achieved by a constriction of the free space forthe inlet of the immersion nozzle part. This constriction may beeffected by flow bodies which are arranged on the broad side of theimmersion nozzle part, or by the inward formation of dents.

In an advantageous way, the constriction has a dimension whose widthcorresponds approximately to the diameter of the upstream tubularimmersion nozzle part, and which corresponds in length to 0.2 to 1.2times its width.

The leading edges and the trailing edges are of sharp-edged constructionand in this case have an angle β from the leading edge and the innerwall of 90 to 150°. It is possible to combine the shaping of theintermediate part and the constriction. It is proposed in the case ofthis combination to match the contour of the bulge of the intermediatepart to the leading edge of the flow element in the second immersionnozzle part.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote similarelements throughout the several views:

FIG. 1 shows a longitudinal section of an immersion nozzle according toan embodiment of the present invention;

FIG. 2 shows a cross-section of an immersion nozzle of FIG. 1 and a flowof metallic-liquid there through;

FIG. 3 shows a cross-section of the immersion nozzle of FIG. 1 after themetallic liquid has entered the melt below the immersion nozzle;

FIG. 4 shows a longitudinal section of an immersion nozzle according toanother embodiment of the present invention;

FIG. 4a shows a detail A of FIG. 4; and

FIG. 5 shows a cross-section of the immersion nozzle of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-3 show immersion nozzle which includes a first immersion nozzlepart 11, an intermediate part 31 and a second immersion nozzle part 21.A central axis is denoted by I.

Using the same item numbers in all the figures, the first immersionnozzle part 11 is fastened via a flange 12 to a melt vessel 41. Anoutlet 42 of the melt vessel 41 may be closed by a plug 43. The firstimmersion nozzle part 11 has a round, oval or else polygonal crosssection and is connected via the intermediate part 31 to the secondimmersion nozzle part 21, which has broad sides 25 which are distinctlylarger than the narrow sides 26. The first immersion nozzle part 11 hasa slot 13 in the region of the intermediate part 31.

The second immersion nozzle part 21 has a mouth 28 which projects into apermanent mold 51, a mouth 28 dipping into the melt S located in thepermanent mold 51. Casting powder P is located on the melt S.

In FIG. 1, the intermediate part 31 has a bulge 34 associated with eachbroad side 25. In the right-hand part of FIG. 1, a first embodiment ofthe bulge 34 is as a spherical shape 35, and a second embodiment in theleft-hand part of FIG. 1 is a tube segment 36.

On the left-hand side of FIG. 1, the bulge 34 directly adjoins the roundimmersion nozzle part 11 in the shape of a tube segment 36. Withreference to a main axis II, shown in FIG. 2 the tube segment 38 mayhave a constant radius or else be of parabolic configuration.

A plan view of the bulge 34, represented here as a tube segment 36, isshown in FIG. 2.

A plan view of the bulge 34 is shown in FIG. 3 as a spherical shape 35.Clearly in evidence is the pointed mouth of the quarter hollow sphere 35in the case of the transition to the broad side 25 of the secondimmersion nozzle part 21.

The first immersion nozzle part 11, represented here as a tube, opens inthe upper part of FIGS. 2 and 3, the slot 13 being located at the mouth.Represented at the start of the slot to both sides of the narrow side 33is the intermediate part 31, which covers the broad sides 32. The narrowside 33 is inclined at an angle of γ to the run-up 22.

The view of the broad side 32 of the intermediate part 31 is representedin FIG. 2. In the central region, the bulge 34 is constructed as a tubesegment 36. The bulge 34 is constructed as a quarter hollow sphere 35 inFIG. 3.

The arrows in FIGS. 2 and 3 represent the velocity vectors of themetallic liquid. It is shown in FIG. 2 how the volume and quantity ofthe melt are reduced in the central region in the flow directiondownstream of the throttle element. The melt flows into the secondimmersion nozzle part 21 in a distinctly expanded fashion with an angleof expansion δ.

In the mouth region of the second immersion nozzle part, the velocityprofile in the region of the narrow side walls has a relatively shapewhich has a low velocity in the mouth center.

In the permanent mold itself (see) (FIG. 3), the velocity vectors have acomponent which permit a portion of the melt to flow back to the bathsurface. Here, they are guided to the middle of the permanent mold 51and guided up the sides again back down in the direction of strandwithdrawal in the center of the permanent mold 51 and also between thebroad side 25 of the immersion nozzle 21 and the and broad side 52 ofthe permanent mold 51.

The narrow side 21 opens towards the mouth of the second immersionnozzle part with reference to the central axis I in a conical fashion atan angle α. This angle α can be clearly greater than the 7° possible inthe case of free jets, and can assume a value of up to 15° (see) (FIG.5).

FIG. 4 shows a flow body 62 and a dent 61 in the shadow of the firstimmersion nozzle 11 in the inlet 22.

In the left-hand side of FIG. 4, the first immersion nozzle part 11 isconstructed as a tube whose end is closed by a seal 27. A tube segment36 is arranged in the inner gore between the seal 27 and the tube 11.The contour 37 is of parabolic configuration. From its mouth, the tubesegment strikes the leading edge of a flow body 62.

In the present case, the leading edge 64 is arranged at an angle of 90°to the inner side of the flow body 62. The trailing edge 65 of this flowbody 62 likewise has an angle β of 90°.

On the right-hand side, the tube 11 is sealed by an inclined surface 38which is led to the inlet 22 of the second immersion nozzle part 21. Theinlet region 22 is constructed as a dent 61. The outer surface of theleading edge 64 has the same angle of inclination as the inclinedsurface 38.

In the present case, the trailing edge 65 has an angle β ofapproximately 45°. The broad side 25 of the second immersion nozzle part21 has the same wall thickness as the dent, and springs outwards in theregion of the trailing edge 65. In the direction of flow downstream ofthe flow bodies 61 and 62, the free space 23 is the same size as thewhole of the second immersion nozzle part as far as its mouth.

FIG. 5 shows the plan view of the section of the second immersion nozzle21, represented in FIG. 4, with the constriction 61, 62. Arranged in theshadow of the first immersion nozzle part 11 in the inlet region 22 ofthe second immersion nozzle part 21 is a flow body 62 having thedimensions of A=l×D. In this case, the length 1 has a value of l=0.2 to1.2×D, corresponding to the diameter D of the tubular first immersionnozzle part 11.

Otherwise than in the preceding FIGS. 2 and 3, in FIG. 5 the angle γ isin the upper range of the possible bevel of γ=0 to 40°. The angle α hasalso been selected to be greater than in FIGS. 2 and 3, it beingpossible for α to be between 0 to 15°.

What is claimed is:
 1. A process for directing a flow of metallic liquidfrom a melt container to a stationary permanent mold through a firstimmersion nozzle part, an intermediate part, and a second immersionnozzle part of an immersion nozzle, the second immersion nozzle parthaving an elongated cross section with broad sides and narrow sides,said process comprising the steps of: a. reducing a central portion ofthe flow of metallic liquid at an inlet region of the second immersionnozzle part with respect to the broad sides of the second immersionnozzle part; b. increasing the angle of expansion of the flow of themetallic liquid at the inlet region for substantially preventing areturn flow of the metallic liquid along the narrow sides of the secondimmersion nozzle part; and c. directing the flow upon leaving the secondimmersion nozzle part with a velocity profile of flow that is smallertoward the central portion of the second immersion nozzle part andlarger toward the narrow sides of the second immersion nozzle part. 2.The process of claim 1, further comprising a step of imparting avelocity component to the flow of liquid exiting the second immersionnozzle that is directed toward the narrow sides of the second immersionnozzle part for ensuring a specific return flow of the melt to a bathlevel in the permanent mold; and setting a quantity of melt added to thebath of the permanent mold such that the melt penetrates the bath in thepermanent mold down to a depth corresponding to a mixing length withinthe range including 0.2 to 4 m with a strand withdraw rate within therange including 1 to 10 m/min.
 3. The process of claim 2, wherein saidstep of setting a quantity of melt comprises setting a quantity of meltadded to the bath of the permanent mold such that the melt penetratesthe bath in the permanent mold down to a depth corresponding to a mixinglength within the range including 0.2 to 2 m with a strand withdraw ratewithin the range including 4 to 5 m/min.
 4. The process of claim 1further comprising a step of directing the flow of metallic liquid intothe bath in the permanent mold down to a depth corresponding to a mixinglength so that velocity vectors of the bath below the mixing length aredirected in the same direction and the same speed as the strand withdrawrate from the permanent mold.
 5. An immersion nozzle for pouringmetallic liquids from a melt container to a bath in a permanent mold,comprising: a first immersion nozzle part connectable to a melt vesselfor receiving the metallic liquids and having a first cross sectioncomprising one of a circular, oval, and polygonal shape; a secondimmersion nozzle part having an inlet section and a mouth and having anelongated second cross section with broad sides an narrow sides, whereinan area of said second cross section is equal to or less than and areaof said first cross section; an intermediate part connecting said firstimmersion nozzle part to said second immersion nozzle part; and acentral axis of said immersion nozzle running through said firstimmersion nozzle part, said second immersion nozzle part and saidintermediate part; said mouth of said second immersion nozzle beinginsertable into the permanent mold so that said mouth is receivable inthe bath; and one of said inlet of said second immersion nozzle part andsaid intermediate part comprises a configuration projecting toward saidcentral axis for reducing a central portion of the flow of metallicliquid at said inlet region of said second immersion nozzle part withrespect to said broad sides of the second immersion nozzle part andincreasing an angle of expansion of the flow of the metallic liquid atsaid inlet region for substantially preventing a return flow of themetallic liquid along said narrow sides of said second innnersion nozzlepart.
 6. The immersion nozzle of claim 5 , wherein said configurationcomprises a concave bulge projecting from one of said broad sides. 7.The immersion nozzle of claim 6, wherein said bulge comprises a quarterhollow sphere.
 8. The immersion nozzle of claim 6, wherein said bulgecomprises a tube segment having a tube axis parallel with said broadsides of said second immersion nozzle part.
 9. The immersion nozzle ofclaim 8, wherein said tube segment comprises a parabolic contour with aportion of said tube segment having a smaller radius being inclinedtoward said inlet of said second immersion nozzle part.
 10. Theimmersion nozzle of claim 5, wherein said intermediate part comprises aseal connecting upper edges of said narrow sides to said first immersionnozzle part, said seal being inclined at an angle within the rangeincluding 0 to 40 degrees.
 11. The immersion nozzle of claim 5, whereinsaid configuration comprises a constriction between said broad sides insaid inlet of said second immersion nozzle part.
 12. The immersionnozzle of claim 11, wherein said constriction comprises dents in thebroad sides extending into a free space between said broad sides. 13.The immersion nozzle of claim 11, wherein said constriction comprises aflow body extending into a free space between said broad sides.
 14. Theimmersion nozzle of claim 11, wherein said first immersion nozzle partcomprises a diameter D and said constriction extends along a directionof flow with a length within the range including 0.2×D to 1.2×D.
 15. Theimmersion nozzle of claim 11, wherein said constriction comprises atleast one of a leading edge and a trailing edge with a corner having anangle within the range including 90 to 150 degrees.
 16. The immersionnozzle of claim 11, wherein said configuration comprises a bulge andsaid constriction comprises a leading edge downstream of said bulge. 17.The immersion nozzle of claim 5, wherein said configuration is arrangedin a portion of said one of said inlet of said second immersion nozzlepart and said intermediate part comprising a first width and wherein adimension of said configuration along the direction of said first widthis smaller than said first width.
 18. The immersion nozzle of claim 17,wherein said intermediate part comprises a top connected to said firstimmersion nozzle part and a bottom connected to said second immersionnozzle part, said configuration being arranged proximate said bottom ofsaid intermediate part.